This invention relates to plastic film handling equipment and is more specifically directed to a machine for transporting a workpiece formed from a web of plastic film material. An example of such a workpiece is a plastic bag, which is produced at a bag machine or similar station and is to be transported to a collection station. The invention is concerned with a rotary wicketter, i.e., a rotary transport device in which an array of vacuum arms, i.e., hollow perforated bars, extend radially out from a rotor hub, and in which vacuum is applied for a portion of the rotation to carry the plastic film workpiece from one station to another.
Vacuum wicketters are widely used in the plastic film trade, and their general construction and operation is well known. The general design and operation of a wicketter can be understood, e.g., from Gaffal U.S. Pat. No. 6,702,277 (Mar. 9, 2004), Stock U.S. Pat. No. 5,074,735 (Dec. 24, 1991), and Sample et al. U.S. Pat. No. 4,668,158 (May 26, 1987). An improved wicketter hub arrangement in which the hub is formed of a synthetic plastic resin is described in Pottorff U.S. Pat. No. 4,877,233 (Oct. 31, 1989), and also in Pottorff U.S. Pat. No. 5,143,367 (Sep. 1, 1992). The conventional wicketter is of metal construction, with a two-part hub assembly and vacuum arms extending outward from the hub. The hub assembly has a rotating main hub, which is secured to the rotating shaft, and a vacuum hub that does not rotate. A vacuum source, i.e., a vacuum pump, connects via a hose to the stationary vacuum hub. The rotary hub has vacuum ports on the side that faces the vacuum hub, and these are arranged so that there is vacuum applied to the rotating arms as they proceed along an arc corresponding to the transport path of the workpieces. There is typically a semicircular opening on the facing side of the vacuum hub for this purpose. In many arrangements, a pair of hubs are used, each with its array of vacuum pickup arms, both mounted on the same rotary shaft or spindle. This allows the workpiece to be gripped on either edge by the vacuum arms and transported to the collection station.
The rotary hub can carry any number of arms, but typically there are six or eight spaced evenly around the body of the hub. The arms can be of any cross section, and these are often hollow extrusions of square or rectangular profile on the part that extends radially out from the hub, but are typically circular in profile in the part that fits into an arm socket in the hub body. Each arm, in its leading side, i.e., in the rotation direction, has a vacuum channel and one or more rows of vacuum openings leading from the hollow interior of the arm. This configuration ensures that vacuum is applied to the workpiece to hold it in place on the arm. Also, the leading surface may be coated with a ceramic material, or may have a wear plate installed on it, to allow for the erosive nature of the plastic film material.
These hollow wicketter vacuum arms have a plug or plate at their radial outward end to seal the interior cavity. These are usually welded or cemented in place, but in some cases are secured by threaded screws, and are not meant to be easily removed.
It is well understood that the manufacture and handling of the plastic film web and products constructed from the film create a significant volume of plastic dust. The dust collects inside the vacuum wicketter, typically inside the vacuum arms and in the rotary hub. If the wicketter is not cleaned at a rather frequent interval, the plastic dust can clog the wicketter and interfere with its effective operation. Typically a cleaning operation involves significant machine down time to remove each arm from the hub, clean the plastic dust from its interior cavity, and then re-install the arm. This involves having to unscrew one or two machine screws that hold each arm in place, and then reinsert and fasten these when the arm is replaced.
It is also necessary from time to time to reset the position of the wicketter hubs along the spindle or shaft. When that occurs, it is necessary first to loosen a locking ring that holds the hub body to the shaft or spindle. When the hub has been moved and re-aligned, the hub lock ring has to be tightened again to secure the hub to the shaft. A screwdriver and/or wrench is needed for this. Also, because the locking ring has a tightening mechanism on one side only, it has a tendency to pinch and may not tighten evenly on the shaft.
It is desired that the process of setting up the wicketter be made as simple and quick as possible to minimize machine downtime and to reduce the number of steps and the number of fastener parts and tools required. It is also desired to facilitate the removal and reinsertion of the vacuum pickup arms so the plastic dust can be cleaned from them without difficulty and without requiring equipment or tools.